This invention relates to bilayer glazing panels and more particularly to a method of forming such panels.
Laminated glazing panels are well known for use as windshields, side and rear windows, and sunroofs in vehicles, architectural glass in buildings including skylights, intrusion security glass, solarium doors and the like. Along with glass, these panels include an energy absorbing plastic layer capable of absorbing a blow from an object without penetration of the glazing panel by the object, thus providing safety to occupants of the surrounding area.
Commercial laminated glazing panels usually have a pane of glass on each side of the energy-absorbing layer. An alternative to this trilayer structure is a bilayer which has a single pane of glass against a plastic inner layer usually of two or more plies. In addition to being lighter in weight, when impact sufficient to break the glass of a bilayer occurs, the danger from glass fragments within a room or vehicle compartment is greatly reduced by the absence of the interior glass layer.
Plasticized polyvinyl butyral is used most as the energy-absorbing layer in the trilayer structures mentioned above. Such polyvinyl butyral contains about 15-30 weight % hydroxyl expressed as polyvinyl alcohol, ("partial PVB") for interaction with the glass to form a tenacious bond in the laminate(along with 0 to 2.5 weight % acetate expressed as polyvinyl acetate with the balance being butyral expressed as polyvinyl butyral). Because of long commercial use in trilayer glazing panels, laminators are quite familiar with the handling and properties of plasticized partial PVB sheet, and it has been proposed for use in bilayers. U.S. Pat. No. 4,937,147 focuses on the bond between partial PVB and polyurethane in a bilayer and U.S. Pat. No. 4,952,457 on the moisture tolerance of plasticized partial PVB sheet in a bilayer. As disclosed in these patents, it is likewise known to use cross-linked polyurethane in bilayers as the damage-resistant inboard surface facing the interior of the vehicle compartment or room containing the bilayer.
While moderately successful, the systems of these patents deal with properties of the plastic components of a bilayer and do not address economical preparation of bilayers on a commercial scale.